There are many instances in which it is necessary or desirable to deploy a battery-powered electronic device into a remote field location. For example, in a military context, electronic devices may be deployed into a combat area that is difficult or dangerous to access. These devices may not be actively needed for months or years, and will therefore spend long periods in a standby mode. Accordingly, the devices need to be able to retain the ability to operate upon command without having lost significant battery power while in standby mode. Achieving this ability may present a problem since the electronics typically draw non-negligible current from the battery while in standby mode, thereby prematurely draining the battery and causing the device to have a short lifespan.
One approach to this problem is to power the devices other than through a battery, such as through transmitting electromagnetic energy to the device in order to activate and power it. Such a solution is found in typical radio frequency identification (RFID) systems. Unfortunately, this solution fails to adequately address the problem of transmitting electromagnetic power to devices in difficult operating environments, such as underwater, underground or in dense urban environments, where electromagnetic waves suffer from reflection, refraction or scattering. This approach also faces the difficulty of transmitting sufficient electromagnetic power to energize a device having moderately large power consumption in the active mode. Another shortcoming encountered with the electromagnetic wave approach, particularly in a military context, is the fact that significant electromagnetic transmissions may be easily detectable by opposing forces.